1. Field of Invention
The present invention relates to a stage device, and particularly to a stage device using an air bearing in a vacuum in an electron beam exposure apparatus or the like.
2. Background Art
In electron beam exposure apparatuses and electron microscopes, a sample is exposed, observed, or measured while being mounted on a stage. For example, an electron beam exposure apparatus performs an exposure process while moving a stage in accordance with exposure data so that a required position on a wafer may be exposed.
A roller stage of cross roller type has been provided as a stage including a mechanical bearing. Regarding this stage, multiple rollers provided in a track between a movable stage and a fixed stage are rolled (rotated) to move the stage.
When such a stage with a mechanical bearing is used in a state where a particle exists on a track, the particle causes strain in the stage mechanism. Such strain degrades the accuracy of stage position detection, and makes it difficult to detect a stage position accurately. Moreover, a particle does not remain at a certain place on the track but moves as the stage moves. This phenomenon hinders replication of the position change of the stage and prediction of a position where to move the stage. Thus, the stage mechanism has difficulty in correcting the position of the stage. Further, in the case where oil is applied to the track and the rollers for lubrication of the track and the prevention of dust generation, particles can be removed to a certain extent while the oil exists, but dust may be generated rapidly when the oil is lost.
In contrast to the stages using mechanical bearings, techniques using air bearings are coming to be studied and used. For example, Japanese Patent Application Publication No. 2006-66589 describes a stage device in an exposure apparatus for use in photolithography. In the stage device, a movable member is supported on a base member in a noncontact manner using a fluid bearing (gas bearing).
When such an air bearing is used, the degradation of accuracy of a stage caused by particles on the track of the stage can be reduced compared to when a mechanical bearing is used.
On the other hand, when an air bearing stage is used, air needs to be supplied for driving a stage mechanism. Usually, the air generated by an air generator is supplied to the stage via air piping made of a PTFE-based material which is usable in a vacuum chamber.
In this case, the air piping in this vacuum chamber moves every time the stage moves, and accordingly is partly bent. Since a moving range of the stage is limited, the air piping is frequently bent nearly at the same portion, and therefore may be ruptured due to fatigue after numerous bending actions. For this reason, the operating life of the entire stage device is determined by a defect of the air piping even if the stage itself has no failure. For example, continuous use of a typical stage device available at present requires replacement of the piping every several years.